[utkarshcloudinary]

No issue. CI speed-up.

Approach

The Composer cache in ci.yml was never used. Every job cached ~/.composer/cache, but Composer on the runner writes to ~/.cache/composer. So each job got "Cache not found" on restore and a "Path Validation Error" on save. This PR fixes the cache, makes PHPCS faster, and cancels superseded PR runs.

• Read the Composer cache path from composer config cache-files-dir in all four jobs, the same way deploy-to-wp-org.yml already does.
• Fix the build matrix cache key. It used the undefined matrix.php, so it should be matrix.php-version. The 7.4 and 8.5 jobs now get separate keys.
• Add a concurrency group that cancels a superseded run when a PR gets a new push. Runs on develop and master pushes are not cancelled.
• Run PHPCS with --parallel=8 through phpcs.xml.dist. This also makes the lint-staged pre-commit hook faster.

Measured results

Data from run 39405988243: attempt 1 (cold cache) and attempt 2 (warm cache). The baseline is earlier develop/PR runs.

• Composer cache: all five jobs now restore it (Cache restored from key: Linux-composer-<job>-...), and the save step no longer shows a path error. The time saved is small: composer install takes about 1.5 to 2.5s with the warm cache and about 3 to 5s before.
• PHPCS in the build jobs: about 25 to 32s on this branch (4 job runs), against about 36 to 62s before (6 job runs on 3 recent runs). Locally, composer lint drops from about 24s to 8s.
• Total wall time is not changed. It stays at about 5.5 min because the E2E job is the critical path, and this PR does not change it.

Follow-ups (not in this PR)

For the E2E job, about 1.5 min is wp-env start and about 1.8 min is the single-worker @serial pass.

• Split @serial specs across a 2-shard matrix, each with its own wp-env.
• Start wp-env with testsEnvironment: false in CI to boot one site instead of two. The E2E and unit setup use the tests containers, so this needs a config and helper change first.

QA notes

• In any run after the first one on a branch, the "Cache Composer" step should log Cache restored from key: Linux-composer-.... The post step should not show "Path Validation Error".
• build (7.4) and build (8.5) should use different cache keys (Linux-composer-7.4-... and Linux-composer-8.5-...).
• Push two commits quickly to a PR. The first run should be cancelled. (Not exercised on this PR.)
• npm run lint:php locally should give the same result as before, only faster.

[gabrielcld2]

Nice job 👍